Getting value from JSON and processing depending on variable type - Scala

Question

I am new to Scala and I need to figure out how to process a JSON depending on two scenarios.

First is where I receive such a JSON: {..."field":[{"count":1,"value":"foo"}]...}
Second scenario is where I receive this kind of JSON: {..."field":"foo"...}

I can not determine when each JSON will come in(it is random). In both scenarios I need to get the field value and store as a String into separate JSON. Second scenario is obvious as it is a String already but I can not figure out how to determine whenever this field is Array or String and if Array then get the "foo" from JSON within it. I know how to access the field as it is a cursor:
val field = cursor.downField("foo").downField("bar").downField("lorem").downField("field")
Below example of my approach which is not working:

if (field.asInstanceOf[String]) {
    rowFiltered.set("field", field.as[String])
} else {
    rowFiltered.set("field", field.as[Seq[field[0]]])
}

Help with determining and assigning will be appreciated.

Looks like it should isInstanceOf rather than asInstanceOf but perhaps that is a typo. — Tim
– Tim, Commented Oct 7, 2021 at 9:45

ccheneson · Accepted Answer · 2021-10-07 09:58:03Z

1

You can use orElse and pass another parsing.

import io.circe._
import io.circe.literal.JsonStringContext


object App {

  final case class MyField(value: String)

  def main(args: Array[String]): Unit = {
    val jsonValue01: Json =
      json"""{
            "hello": "world",
            "field":[{"count":1,"value":"foo01"}],
            "foo" : "bar"
            }"""

    val jsonValue02: Json =
      json"""{
            "hello": "world",
            "field": "foo02",
            "foo" : "bar"
            }"""

    implicit val decodeField: Decoder[MyField] = new Decoder[MyField] {
      final def apply(c: HCursor): Decoder.Result[MyField] =
        for {
          foo <- c.downField("field").downN(0).downField("value").as[String]
                  .orElse(c.downField("field").as[String])
        } yield {
          new MyField(foo)
        }
    }

    val myField01 = jsonValue01.as[MyField]
    val myField02 = jsonValue02.as[MyField]

    println(myField01) //Right(MyField(value = foo01))
    println(myField02) //Right(MyField(value = foo02))

  }
}

answered Oct 7, 2021 at 9:58

ccheneson

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4 Comments

Mateusz Osinski Over a year ago

Thank you for your input! I'm facing now the following error with your approach: value orErase is not a mamber of io.circe.Decored.Result[String]

Mateusz Osinski Over a year ago

I've tried to change the input values, as I have a hcursor as input and tried to do val field = data.hcursor.downField('foo').downField('bar').as[io.circe.Json] but received erros as well

ccheneson Over a year ago

It's not orErase but orElse

Mateusz Osinski Over a year ago

Imported import cats.syntax.either._ and works fine, thank you, will verify if the data will be extracted correctly, thanks one again!

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